The invention relates to a transport system. From German Patent DE 40 39 265 C2, a transport system is known in which the feeding and/or discharging of workpiece carriers at machining units is performed with the aid of a phased conveyor. The conveyor belt of the phased conveyor is divided by cams into segments in which workpiece carriers are disposed. There are workpiece carriers with unmachined or machined parts and/or component units in the segments upstream and downstream of the machining unit, respectively. The conveying is done in accordance with a speed profile that recurs once per phase. This serves to increase the throughput of workpiece carriers. A speed profile can be shown for instance in the form of a speed and travel graph or a speed and time graph. Beginning at the zero speed, the speed of the phased conveyor increases to a certain value and then returns to zero. The speed profile for the phased conveyor is generated by a frequency inverter, a braked rotary current motor, a worm gear, and a disk cam gear. With the frequency inverter, the braked rotary current motor is operated at different but in each case constant rotary speeds, or rpm. The worm gear converts the rpm of the rotary current motor into a lower driven rpm. Such a gear is required in all transport systems that use rotary current motors, since the rotary speeds of a rotary current motor are relatively high. It is the disk cam gear that for the first time converts the constant driven rpm of the worm gear into a driving rpm for the phased conveyor, and this driving rpm is directly proportional to the speed profile.
During the machining cycle, the phased conveyor is at a standstill. It conveys articles only whenever the end of machining is reached and the outlet is empty. It is always disadvantageous, however, if after the machining there are no workpiece carriers at the inlet. Either the phased conveyor conveys an empty segment, which means that in the machining unit the parts and/or component groups of a missing workpiece carrier are machined, or the phased conveyor stops because it is waiting for an unmachined machining unit. During this period, no workpiece carriers are discharged. In the workpiece carrier throughput, a gap has occurred that can no longer be made up for.
Employing the principle of the phased conveyor to the entire transport system including the main conveyor way and the feeder conveyor way and discharge conveyor way would mean that the individual machining units would no longer be connected to a flexible transfer system but would be firmly chained together. This is because in that case the workpiece carriers would be trapped between cams or within segments and could thus no longer be transported flexibly.
The length of the phased conveyor is also an integral multiple of the length of one segment, which means that the length of the phased conveyor cannot be designed to be highly variable.
In addition to the known transport system, there are still others that in order to achieve a higher workpiece carrier throughput operate at a higher conveyor way speed. This has the disadvantage, however, that workpiece carriers run up at the correspondingly higher speed against stoppers or workpiece carriers that are at a stop. Thus dampers or additional time are required to calm the workpiece carrier, and once again this causes delays.